The present invention relates to frequency oscillators, and more particularly to an oscillation circuit having a compensation unit and an electronic device containing such an oscillation circuit.
Frequency oscillators are widely used in analog circuits, mainly for converting DC energy into AC energy. A ring-structured oscillator is the simplest and easiest to implement. FIG. 1 shows a conventional ring oscillator including three or more odd-numbered stages of delay elements. Each of the delay elements introduces a delay and a phase to maintain the desired oscillator frequency.
Since a conventional oscillator is susceptible to temperature and fabrication process variations, the oscillator frequency may deviate more than ±40% from the normal frequency without any compensation scheme. The main factor for the deviation includes the threshold voltage drift, the gate capacitance and other parameters of the transistors (e.g., MOS transistors) due to process variations, changes of carrier mobility and device characteristics due to temperature variations. In addition, various passive devices within the oscillator may vary with the change in processes and in technology.
In order to maintain a stable and accurate oscillator frequency, the conventional approach is to externally trim the oscillator by performing an external calibration in combination with some digital control logic to adjust the oscillator frequency. FIG. 2 is a simplified circuit diagram of an external calibration mode oscillation circuit of the prior art. It can be seen that the conventional approach has several drawbacks. For example, a reference clock and a digital control circuit are required.
The conventional approach without external calibration is not able to meet the required frequency accuracy. Furthermore, an external calibration circuit requires an additional reference clock and digital control circuit that will increase costs and complexity to the oscillator.
Therefore, there is a need for a novel oscillator circuit and an electronic device including the same that provides a stable oscillator frequency across temperature and fabrication process variations.